1. Field of the Invention
The present invention relates to a film carrier tape on which electronic devices such as IC Chips and LSI Chips are to be mounted.
2. Description of the Related Art
Development of the electronics industry has been accompanied by sharp demand for printed-circuit boards for mounting electronic devices thereon, such as IC (Integrated Circuits) Chips and LSI (Large-Scale Integrated circuits) Chips. Manufacturers have attempted to realize small-size, light-weight, and high-function electronic equipment, which has long been desired. To this end, manufactures have recently come to employ a film carrier tape, such as a COF tape, a TAB tape, a T-BGA tape, or an ASIC tape. Use of film carrier tapes has become increasing important, especially for manufacturers of personal computers, cellular phones, and other electronic equipment employing a liquid crystal display (LCD) that must have high resolution and flatness, as well as a narrow screen-frame area.
Such a film carrier tape for mounting electronic devices thereon is produced by providing, for example, sprocket holes for conveying the film carrier tape, device holes, and other holes in an insulating layer made of polyimide; subsequently providing copper foil on a surface of the insulating layer by the mediation of an adhesive layer; patterning the copper foil while the insulating layer is conveyed with the sprocket holes, to thereby form a wiring pattern; and subsequently forming a solder resist layer on the wiring pattern in accordance with needs.
After completion of the steps of producing a film carrier tape for mounting electronic devices thereon, there is performed a reeling step in which the produced film carrier tape is reeled with an embossed spacer film which has concavo-convex surface form.
For example, in the solder resist curing step, a solder resist coating layer formed on the wiring pattern is thermally cured to some extent, and the thus-treated film carrier tape is reeled with an embossed spacer film and heated again so as to completely cure the solder resist coating layer, thereby forming a solder resist layer.
Meanwhile, there has arisen demand for considerably reducing the thickness of such a film carrier tape itself for mounting electronic devices thereon, in order to keep pace with a trend for downsizing of electronic devices. Thus, in recent years, a COF (chip on film) tape employing a relatively thin insulating layer has been proposed.
However, the aforementioned COF tape having a thin insulating layer causes deformation of sprocket holes during conveyance of the tape, since wiring patterns and similar elements are formed on the aforementioned film carrier tape for mounting electronic devices thereon while the insulating layer is continuously conveyed. Thus, the COF tape has drawbacks that wiring patterns, solder resist patterns, etc. cannot be formed on predetermined positions with high precision and that electronic parts cannot be mounted with high precision.
In order to overcome the aforementioned drawbacks, there has been provided a tape structure in which a dummy wiring portion (metallic layer) is provided around each sprocket hole in a discrete manner, whereby the tape maintains suitable mechanical strength during conveyance thereof (see, for example, Japanese Patent Application Laid-Open (kokai) No. 2002-299385 (FIG. 1)).
However, the aforementioned film carrier tape for mounting electronic devices thereon provided with a dummy wiring portion also has a drawback in that wavy deformation is generated along the opposite longitudinal edges of the both sides thereof during the final production stage as the film carrier tape for mounting electronic devices thereon.
Such wavy deformation is not observed in customary film carrier tape products employing no dummy wiring portion around sprocket holes and is considered to be generated for the following reason. Specifically, under application of pressure to the film carrier tape (e.g., in a reeling step employing an embossed spacer film), differences in physical properties between the metallic layer and the insulating layer; e.g., differences in linear expansion coefficient, tensile strength, percent elongation, and similar properties, complicatedly affect the film carrier tape for mounting electronic devices thereon upon treatment in production steps such as heating or cooling.
Such a film carrier tape for mounting electronic devices thereon having wavy deformation cannot be conveyed and positioned smoothly by use of a pin roller or a similar device in a semiconductor chip mounting line. As a result, failure such as mount failure of electronic parts is induced, leading to failure of final products, which is problematic.